The image diagnosis apparatus, such as NMR imaging apparatus and X-ray CT apparatus, fundamentally comprises data collecting means for collecting projection data pertaining to a desired section of a subject to be examined by the use of the nuclear magnetic resonance phenomena or X ray, image reconstructing means for reconstructing the sectional image of the subject on the basis of the collected projection data, and image display means for displaying the reconstructed image.
FIG. 9 shows an NMR imaging apparatus which is an example of the foregoing type of image diagnosis apparatus. The NMR imaging apparatus has a magnet section which is configured so that a static magnetic field coil 1 and a gradient magnetic field coil 2 (made up of coils for the individual x-, y- and z-axes) are disposed in place. The static magnetic field coil 1 is energized by a static magnetic field coil driving section 3 with the gradient magnetic field coil 2 by a gradient magnetic field coil driving section 4, so that in the inside space of the magnet there are created a static magnetic field being uniform in the z-axis direction and gradient magnetic fields oriented in the same direction as that of the static magnetic field but each having a linear gradient in each direction of the x-, y- and z-axes. An exciting coil 5 and a detecting coil 6 are disposed in the magnetic field of the magnet section while keeping a rotational angle of 90.degree. therebetween about the z-axis, the former coil being energized by an exciting coil driving section 7 to apply high-frequency electromagnetic wave pulses to a subject (not shown) placed in the inside space of the magnet with the latter coil detecting an NMR signal coming from a desired spot of the subject and applying it to an analog-to-digital converting section (hereinafter referred to as A-D converting section) 8. This A-D converting section 8 converts the detection signal into a digital signal and applies it to a control/image processing section 9. This control/image processing section 9 is the center of control and image processing over the whole NMR imaging apparatus and is made of a computer. The control/image processing section 9 is equipped with an external memory 10. The control/image processing section 9 controls the static magnetic field coil driving section 3, gradient magnetic field coil driving section 4, exciting coil driving section 7 and A-D converting section 8 to collect the NMR signal of the subject, and stores the obtained NMR signal (raw data) in the external memory 10. Further, the control/image processing section 9 reconstructs an image representative of a subject's section on the basis of the raw data stored in the external memory 10 and stores the reconstructed image in the external memory 10 again. Further, the control/image processing section 9, in accordance with an instruction from an operator which is given through an operator console 15, reads out the reconstructed image from the external memory 10 and applies it through a display control section 11 to a display unit 14 where it is displayed. At this stage, a window level and a window width for image displaying are regulated for the purpose of making the brightness and gradation of the displayed image adequate.
In the NMR imaging apparatus, the value of the pixal data forming the reconstructed image and its range of variation, i.e. the brightness and gradation of the reconstructed image, vary depending on the system of data collection (pulse sequence), and further, where imaging is carried out using the multiecho method, since the intensity of each of a plurality of echo signals measured in succession becomes progressively weak, the brightness and gradation of each reconstructed image based on each echo vary. To display several reconstructed images differing in brightness and gradation in easily-observable form, it is necessary to regulate each window level and window width adequately so that each image can be displayed with uniform brightness and gradation. Further, also in other types of image diagnosis apparatus such as X-ray CT apparatus, where the brightness and gradation vary from one reconstructed image to another, the window level and window width must be regulated similarly. Hitherto, such a regulation operation for the window level and window width was very complicated because it was performed by an operator with respect to each reconstructed image.